Display device and method of manufacturing the same

ABSTRACT

A display device comprises a first plastic substrate, a first adhesion layer formed in a first region of the first plastic substrate, the first region being a region where a pixel region is to be formed thereon, a second adhesion layer formed in a peripheral region outside of the first region of the first plastic substrate, a first thin glass layer formed on the first and second adhesion layers, a plurality of active elements formed on the first thin glass layer in one-to-one relation with a plurality of pixels, a display part formed on the first thin glass layer, the display part corresponding to the pixel region and being driven by the plurality of active elements, and an opposing substrate formed over the display part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2002-084924, filed Mar. 26,2002, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a display device and a method ofmanufacturing the same.

2. Description of the Related Art

An active matrix type display device in which an active element such asa thin-film transistor (TFT) is placed in each pixel can realize ahigh-quality, flat display device. In a display part of this activematrix type display device, it is possible to use, e.g., a liquidcrystal which functions as a light shutter, an organic EL which emitslight, or an electrophoretic element encapsulated in a microcapsule.These active matrix type display devices can be made thin and light inweight, so they are optimum for portable information apparatuses such asa notebook model personal computer and PDA (Portable DigitalAssistance).

In a TFT used as an active element, a semiconductor film made of, e.g.,amorphous silicon, polycrystalline silicon, crystalline silicon in whichlattice continuity is obtained in the grain boundary, or single-crystalsilicon is used as an active layer. In the fabrication of these TFTs, toimprove the film quality of a semiconductor film, gate insulating film,and the like, a process temperature of about 250 to 350° C. is requiredfor amorphous silicon, and about 400 to 650° C. for highly crystallinesilicon such as polycrystalline silicon. Since this restricts thesubstrate material, glass substrates such as non-alkaline glass havebeen conventionally used.

Portable information apparatuses will be widely used with thedevelopment of radio networks in the future, so display devices arerequired to be made thinner and lighter in weight. To meet thisrequirement, active matrix type display devices using a plasticsubstrate instead of a glass substrate are proposed.

As an example of these active matrix type display devices using aplastic substrate, a method is reported in which a TFT is formed at as alow process temperature as possible by improving the heat resistance ofa plastic substrate. Since the specific gravity of a plastic substrateis half that of a glass substrate or less, the weight of the displaydevice can be reduced. In addition, the flexibility of plastic makes thedisplay device bendable, and this increases the impact resistance.

Unfortunately, a plastic substrate not only has a low heat resistance ofabout 100° C. to 200° C. but also deforms by moisture absorption. Also,the coefficient of linear expansion of a plastic substrate is larger byan order of magnitude than that of a glass substrate. These tendenciesare particularly conspicuous in a transparent plastic substratenecessary for a display device. For these reasons, peeling ordisconnection occurs when active elements and the like are formed on aplastic substrate. Additionally, the mask alignment accuracy lowersbecause layers of active elements are stacked on a plastic substratewhich deforms. When a plastic substrate is used, therefore, it isimpossible to form such high-accuracy patterns as formed when activeelements and the like are formed on a glass substrate. Also, the use ofa plastic substrate lowers the performance of pixel switches and drivingcircuits in a display part using TFTs. Furthermore, when a plasticsubstrate is used, many limitations are imposed on usable materialsbecause cracks are easily formed if brittle metals or insulatingmaterials are used.

As another example of the active matrix type display devices using aplastic substrate, a method in which TFTs formed on a glass substrate orsilicon substrate are transferred onto a plastic substrate is proposedin, e.g., Jpn. Pat. Appln. KOKAI Publication No. 2001-7340 (U.S. Pat.No. 5,834,327). This conventional transfer method will be explainedbelow with reference to FIGS. 1A to 1E.

First, as shown in FIG. 1A, a separation layer 1302 such as aninsulating film which functions as an etching stopper is formed on anelement formation substrate 1301 made of, e.g., glass. On thisseparation layer 1302, elements 1303 such as TFTs 1308 and electrodes1309 are formed using a conventional process.

Next, as shown in FIG. 1B, a temporary adhesion layer 1304 havingadhesion properties is formed on an intermediate substrate 1305, and theelements 1303 formed on the element formation substrate 1301 are bondedto this intermediate substrate 1305 via the temporary adhesion layer1304.

As shown in FIG. 1C, the element formation substrate 1301 is removed byetching or the like so that the separation layer 1302 remains.

As shown in FIG. 1D, an adhesion layer 1306 having adhesion propertiesis formed on a final substrate 1307 to be transferred which is made ofplastic. The separation layer 1302 is bonded to this final substrate1307 via the adhesion layer 1306.

Finally, as shown in FIG. 1E, the temporary adhesion layer 1304 is,e.g., solved by a solvent to transfer the elements 1303 from theintermediate substrate 1305 onto the final substrate 1307.

In the above transfer method, glass or the like having high heatresistance can be used as the material of the element formationsubstrate 1301. Hence, the method can presumably form high-performanceTFTs with high accuracy.

In this method, the element formation substrate 1301 is completelyremoved. Therefore, if the separation layer 1302 which remains has holesor if an excessively thin region is formed in this separation layer 1302and etched together with the element formation substrate 1301, there isa possibility that the elements 1303 are damaged. Since the possibilityof this damage is particularly high in large-screen, active matrix typedisplay devices, the yield of such display devices may lower.

In addition, a liquid crystal or organic EL used as a display partsignificantly deteriorates because plastic used as the final substrate1307 allows easy permeation of water and oxygen. Accordingly, it isnecessary to stop water and oxygen as much as possible by forming, e.g.,an inorganic barrier layer, which stops gases, on the plastic substrate.

As described above, it is conventionally difficult to obtain an activematrix type display device in which active elements can be formed withhigh yield by using a plastic substrate which is light in weight.Therefore, it is being desired to realize an active matrix type displaydevice in which active elements can be formed with higher yield by usinga plastic substrate which is light in weight, and realize a method ofmanufacturing the same.

BRIEF SUMMARY OF THE INVENTION

A display device according to a first aspect of the invention is adisplay device comprising:

-   -   a first plastic substrate;    -   a first adhesion layer formed in a first region of the first        plastic substrate, the first region being a region where a pixel        region is to be formed thereon;    -   a second adhesion layer formed in a peripheral region outside of        the first region of the first plastic substrate;    -   a first thin glass layer formed on the first and second adhesion        layers;    -   a plurality of active elements formed on the first thin glass        layer in one-to-one relation with a plurality of pixels;    -   a display part formed on the first thin glass layer, the display        part corresponding to the pixel region and being driven by the        plurality of active elements; and    -   an opposing substrate formed over the display part.

A display device according to a second aspect of the invention is adisplay device comprising:

-   -   a first plastic substrate provided for at least a pixel region;    -   a third plastic substrate provided for a peripheral region        outside of the pixel region;    -   an adhesion layer formed at least on the first plastic        substrate;    -   a first thin glass layer formed on the adhesion layer;    -   a plurality of active elements formed on the first thin glass        layer in one-to-one relation with a plurality of pixels;    -   a display part formed on the first thin glass layer, the display        part corresponding to the pixel region and being driven by the        plurality of active elements; and    -   an opposing substrate formed over the display part.

A display device manufacturing method according to a third aspect of theinvention comprises:

-   -   forming active elements in one-to-one relation with pixels on an        element formation substrate made of glass;    -   thinning the element formation substrate by polishing after the        forming the active elements;    -   bonding the element formation substrate to a plastic substrate        via a first adhesion layer in a pixel region and via a second        adhesion layer in a peripheral region outside of the pixel        region; and    -   opposing the element formation substrate with an opposing        substrate to form a display part driven by the active elements        and displaying an image in units of pixels.

A display device manufacturing method according to a fourth aspect ofthe invention comprises:

-   -   forming active elements in one-to-one relation with pixels on an        element formation substrate made of glass;    -   thinning the element formation substrate by polishing after the        forming the active elements;    -   bonding a first plastic substrate to the element formation        substrate at least in a pixel region via an adhesion layer, and        bonding a third plastic substrate to the element formation        substrate or the first plastic substrate in a peripheral region        outside of the pixel region via the adhesion layer; and    -   opposing the element formation substrate with an opposing        substrate to form a display part driven by the active elements        and displaying an image in units of pixels.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIGS. 1A to 1E are sectional views showing the manufacturing steps of aconventional active matrix type display device step by step;

FIG. 2A is a plan view of an active matrix type display device accordingto the first embodiment of the present invention;

FIG. 2B is a sectional view taken along a line 2B-2B in FIG. 2A;

FIGS. 3A to 13B are views showing the manufacturing steps of the activematrix type display device according to the first embodiment step bystep, in which views having suffix A are plan views, and views havingsuffix B are sectional views taken along lines designated by numberssuffixed with B in the corresponding plan views;

FIG. 14A is a plan view showing the element arrangement of the activematrix type display device of the first embodiment;

FIG. 14B is a sectional view taken along a line 14B-14B in FIG. 14A;

FIG. 15 is a schematic view for explaining the flexibility of an activematrix type display device of the present invention;

FIG. 16A is a plan view of an active matrix type display deviceaccording to the second embodiment;

FIG. 16B is a sectional view taken along a line 16B-16B in FIG. 16A;

FIG. 17A is a plan view of an active matrix type display deviceaccording to the third embodiment;

FIG. 17B is a sectional view taken along a line 17B-17B in FIG. 17A;

FIG. 18 is a sectional view of an active matrix type display deviceaccording to the fourth embodiment;

FIG. 19 is a sectional view of an active matrix type display deviceaccording to the fifth embodiment;

FIG. 20A is a plan view of an active matrix type display deviceaccording to the sixth embodiment;

FIG. 20B is a sectional view taken along a line 20B-20B in FIG. 20A;

FIGS. 21 to 23 are sectional views showing the manufacturing steps ofthe active matrix type display device according to the sixth embodimentstep by step;

FIGS. 24A to 29B are views showing the manufacturing steps of the activematrix type display device according to the sixth embodiment step bystep, in which views having suffix A are plan views, and views havingsuffix B are sectional views taken along lines designated by numberssuffixed with B in the corresponding plan views;

FIG. 30A is a plan view of an active matrix type display deviceaccording to the seventh embodiment;

FIG. 30B is a sectional view taken along a line 30B-30B in FIG. 30A;

FIG. 31A is a plan view of an active matrix type display deviceaccording to the eighth embodiment;

FIG. 31B is a sectional view taken along a line 31B-31B in FIG. 31A;

FIG. 32A is a plan view of an active matrix type display deviceaccording to the ninth embodiment;

FIG. 32B is a sectional view taken along a line 32B-32B in FIG. 32A;

FIG. 33 is a sectional view of an active matrix type display deviceaccording to the 10th embodiment;

FIG. 34 is a sectional view of an active matrix type display deviceaccording to the 11th embodiment;

FIG. 35 is a sectional view of an active matrix type display deviceaccording to a modification of the 11th embodiment;

FIG. 36 is a sectional view of an active matrix type display deviceaccording to another modification of the 11th embodiment;

FIG. 37A is a plan view showing the element arrangement of an activematrix type display device according to the 12th embodiment; and

FIG. 37B is a sectional view taken along a line 37B-37B in FIG. 37A.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments will be described in detail below with reference to theaccompanying drawings.

(First Embodiment)

The arrangement of an active matrix type display device of the firstembodiment is shown in FIGS. 14A and 14B. As indicated by a largerectangle of a dotted-line in FIG. 14A, a region on a substrate isdivided into a pixel region and peripheral region. In the pixel region,active elements such as TFTs and pixel electrodes connected to theseelements are formed into an array (not shown). In the peripheral region,a connecting pad electrode for connecting interconnections inside thesubstrate and interconnections extracted to the outside of the substrateis formed. Regions which are indicated by small rectangles of adotted-line and in which a scanning line driver and signal line driverare formed are included in the pixel region in this embodiment. However,these regions may be formed in the peripheral region. In FIG. 14A, thesedrivers are formed in the peripheral region.

As shown in FIGS. 2A and 2B, the active matrix type display device ofthis embodiment includes a first plastic substrate 104, a first adhesionlayer 103 formed on the first plastic substrate 104, and a first thinglass layer 101 having a thickness of 150 μm or less and formed on thefirst adhesion layer 103.

The first adhesion layer 103 has a pixel region adhesion layer 1002formed in the pixel region and a peripheral region adhesion layer 1001formed in the peripheral region around the pixel region on the firstplastic substrate 104. The glass transition temperature of the pixelregion adhesion layer 1002 is 30° C. (inclusive) to 80° C. (inclusive).The glass transition temperature of the peripheral region adhesion layer1001 is higher by 10° C. or more than that of the pixel region adhesionlayer 1002, and is 80° C. (inclusive) to 200° C. (inclusive).

On the first thin glass layer 101, an active element circuit region 102,a connecting pad electrode 110 connected to the active element circuitregion 102, and a liquid crystal layer 109 (display part) are formed.This liquid crystal layer 109 is driven by the active element circuitregion 102 in units of pixels. The connecting pad electrode 110 isformed on the peripheral region of the first glass layer 101.

Also, a second thin glass layer 105 is formed over the liquid crystallayer 109, a second adhesion layer 106 is formed on the second thinglass layer 105, and a second plastic substrate 107 is formed on thesecond adhesion layer 106. A common electrode 205 is formed on thatsurface of the second thin glass layer 105, which opposes the liquidcrystal layer 109.

The thickness of the second thin glass layer 105 is 150 μm or less. Thesecond adhesion layer 106 has a pixel region adhesion layer 1002 andperipheral region adhesion layer 1001. The pixel region adhesion layer1002 is formed in the pixel region and has a glass transitiontemperature of 30° C. (inclusive) to 80° C. (inclusive). The peripheralregion adhesion layer 1001 is formed in the peripheral region around thepixel region on the second thin glass layer 105, and has a glasstransition temperature which is higher by 10° C. or more than that ofthe pixel region adhesion layer 1002, and is 80° C. (inclusive) to 200°C. (inclusive).

In this embodiment, in the pixel region, the glass transitiontemperature of the adhesion layer (pixel region adhesion layer 1002)between the plastic substrate and thin glass layer is lowered. In theperipheral region around the pixel region, the glass transitiontemperature of the adhesion layer (peripheral region adhesion layer1001) is raised.

In the pixel region, the glass transition temperature is low and henceeasily reached at a temperature slightly higher than a room temperature.At temperatures equal to or higher than this glass transitiontemperature, the adhesion layer softens, and this permits a differenceproduced by bending or the like between the thin glass layer and plasticsubstrate. This reduces the stress to the thin glass layer and preventsproblems such as destruction. Even at temperatures lower than the glasstransition temperature, the soft adhesion layer allows easy deformation,and this improves the impact resistance.

In the peripheral region, the glass transition temperature is high, andthis suppresses deformation of the plastic substrate and preventscracking of the thin glass layer on the edges. This can also preventthermal stress when a flexible substrate is connected to the connectingpad electrode in the peripheral region via an anisotropic conductivelayer at a temperature of about 200° C.

A method of manufacturing the active matrix type display device of thisembodiment will be explained below with reference to FIGS. 3A and 3B toFIGS. 13A and 13B.

As shown in FIGS. 3A and 3B, an active element circuit region 102 isformed in a pixel region of a first non-alkaline glass substrate 201about 0.7 mm thick. This active element circuit region 102 has a TFTarray using low-temperature polysilicon as an active layer andperipheral driver circuits. In addition, a connecting pad electrode 110for interconnections inside and outside the substrate is formed in aperipheral region.

As shown in FIGS. 4A and 4B, a seal 108 is so formed as to surround thepixel region. This seal 108 is drawn with a dispenser by using anepoxy-based adhesive. The connecting pad electrode 110 is extended tothe outside of the seal 108. An injection hole 204 for injecting aliquid crystal can be formed in the seal 108. However, a liquid crystalcan also be injected without using an injection hole.

As shown in FIGS. 5A and 5B, a common electrode 205 made of atransparent conductive film such as ITO (Indium Tin Oxide) is formed bysputtering or the like on a second non-alkaline glass substrate 202about 0.7 mm thick. This second non-alkaline glass substrate 202 and thefirst non-alkaline glass substrate 201 having the active element circuitregion 102 and connecting pad electrode 110 formed on it are coupled andbonded by hardening the seal 108, such that the common electrode 205 andactive element circuit region 102 oppose each other. Although not shownin the drawings, an alignment films are formed on the pixel electrode102 and the common electrode 205, followed by rubbing. A good alignmentfilm can be obtained at a processing temperature of 200° C. When athermosetting type adhesive is used as the seal 108, this seal 108 ishardened at about 180° C. to 220° C. However, no problem arises becausethe glass substrates having high heat resistance are used. Anultraviolet ray curable adhesive for main sealing may be used as theseal 108.

Next, the two non-alkaline glass substrates are thinned by polishing. Inthis embodiment, as shown in FIGS. 6A and 6B, the first non-alkalineglass substrate 201 on which the active element circuit region 102 isformed is first polished. This polishing is performed by chemicaletching using a hydrofluoric-acid-based etchant, with the secondnon-alkaline glass substrate 202 and the side surfaces protected by achemical-resistant sheet (not shown) or the like. Note that the thinfilm may be formed by mechanical polishing or chemical mechanicalpolishing (CMP).

In FIGS. 6 through 8, only the substrate 101 is polished, but both ofthe substrate 101 and 202 can be simultaneously polished. This makes themanufacturing process shorter.

When polishing of glass is performed, the material protecting thesurroundings need not be a cover sheet. For example, glass polishing canbe performed by temporarily fixing the substrates to a jig such as anappropriate plate member made of glass, hard plastic, metal, or ceramic,and the substrates can be removed from the jig after being polished.When the polished surface is bonded to a plastic substrate explainedlater with the substrate fixed to the jig, no mechanical force isapplied to the thinned glass substrate. This effectively improves theyield.

The first non-alkaline glass substrate 201 is thinned to form a firstthin glass layer 101 about 50 μm thick. That is, the first non-alkalineglass substrate 201 is not completely removed, but the glass layer isleft behind as the first thin glass layer 101. This leaves no damage byremoval of the first non-alkaline glass substrate 201 in the activeelement circuit region 102, so the mechanical strength can bemaintained.

The thickness of the thinned glass is preferably 150 μm or less inaccordance with the conditions such as the polishing accuracy,mechanical strength, and internal stress during the formation of activeelements. If this thickness is more than 150 μm, the glass looses itsflexibility to bending and easily cracks. If the glass thickness is toosmall, permeation of water and the like from the plastic substratecannot be stopped, and this lowers the reliability. Therefore, the glassthickness is favorably about 1 μm or more.

As shown in FIGS. 7A and 7B, the first thin glass layer 101 and a firstplastic substrate 104 made of 0.1-mm thick PES (polyethersulfone) arebonded via a first adhesion layer 103. In this first adhesion layer 103,the characteristics of a peripheral region adhesion layer 1001 aredifferent from those of a pixel region adhesion layer 1002. Theperipheral region is a region which is outside the seal 108 and whichhas the edges and the region in which the connecting pad electrode 110is formed.

In this embodiment, Photolec 720 manufactured by Sekisui Chemical Co.,LTD. or TB3042 manufactured by THREE BOND CO., LTD. is used as the pixelregion adhesion layer 1002. Photolec 720 is an allyl-based ultravioletray curable adhesive having a glass transition temperature of about 47°C. TB3042 is an acryl-based ultraviolet ray curable adhesive having aglass transition temperature of about 60° C.

As the peripheral region adhesion layer 1001, Structbond UC seriesmanufactured by Mitsui Chemicals Inc. or 3025G manufactured by THREEBOND CO., LTD. is used. The glass transition temperatures of StructbondUC series and 3025G are about 109° C. and about 140° C., respectively.

The first adhesion layer 103 is formed to have a thickness of about 10μm to 50 μm and hardened by irradiation with ultraviolet rays throughthe plastic substrate at a room temperature.

The pixel region adhesion layer 1002 desirably has a glass transitiontemperature of 30° C. (inclusive) to 80° C. (inclusive). For example, itis possible to use an acryl-based ultraviolet ray curable adhesive,allyl-based ultraviolet ray curable adhesive, thermosetting acryl-basedadhesive, or thermosetting allyl-based adhesive.

The peripheral region adhesion layer 1001 desirably has a glasstransition temperature which is higher by 10° C. or more than that ofthe pixel region adhesion layer 1002 and is 80° C. (inclusive) to 200°C. (inclusive). For example, it is possible to use an allyl-basedultraviolet ray curable adhesive, epoxy-based ultraviolet ray curableadhesive, or thermosetting epoxy-based adhesive.

Both the peripheral region adhesive 1001 and pixel region adhesive 1002are preferably photo-setting type adhesives, since deformation uponadhesion is small. However, two-part adhesives, thermosetting typeadhesives, or hot-melt type adhesives can also be used by properlyselecting materials and conditions.

Since the peripheral region has no pixel, the peripheral region adhesionlayer 1001 may be opaque, so the glass transition temperature may beraised by mixing fillers or the like. The glass transition temperatureof the peripheral region adhesion layer 1001 is preferably higher by 10°C. or more than that of the pixel region adhesion layer 1002. Note thatthe peripheral region need not completely surround the pixel region,i.e., the peripheral region may be configured to surround the two orthree sides, including the side on which the connecting pad electrode isformed, of the pixel region.

As the first plastic substrate 104, it is possible to use, e.g.,polyether sulfone (PES), polyethylene naphthalate (PEN), polycarbonate(PC), or a polyolefin-based polymer such as cycloolefin polymer, acrylicresin, liquid crystal polymer, reinforced plastic mixed with aninorganic material, or polyimide. It is possible to appropriately selecta thermoplastic resin, thermosetting resin, crystalline resin, oramorphous resin. Transparent or opaque plastic can also be used. PES orArton which is a polyolefin-based resin manufactured by JSR Corporationis suitable for a liquid crystal because each material has small opticalanisotropy and small birefringence. Also, an amorphous transparent resinis favored because its isotropy and flexibility are high. Note that theplastic substrate may be coated with a resin or inorganic film.

As shown in FIGS. 8A and 8B, the second non-alkaline glass substrate 202is thinned by polishing to form a second thin glass layer 105. After therear surface of the first plastic substrate 104 and the side surfacesincluding the first adhesion layer 103 and first thin glass layer 101are protected with a chemical-resistant sheet (not shown), chemicaletching is performed in the same manner as for the first non-alkalineglass substrate 201. The polishing method can be mechanical polishing orCMP. The thickness of the second thin glass layer 105 is preferablyequivalent to that of the first thin glass layer 101, and is about 50 μmin this embodiment.

As shown in FIGS. 9A and 9B, a second plastic substrate 107 is bonded tothe second thin glass layer 105 via a second adhesion layer 106. Thissecond adhesion layer 106 also includes a peripheral region adhesionlayer 1001 and pixel region adhesion layer 1002 having propertiesanalogous to those of the first adhesion layer 103. That region of thesecond thin glass layer 105, which is outside the seal 108 is bonded tothe second plastic substrate 107 by at least the peripheral regionadhesion layer 1001.

In this embodiment, Structbond UC series manufactured by MitsuiChemicals Inc. is used as the peripheral region adhesion layer 1001, andTB3042 manufactured by THREE BOND CO., LTD. is used as the pixel regionadhesion layer 1002. The thickness of the adhesion layer 106 is 10 μm to50 μm. The second plastic substrate 107 is 0.1-mm thick PES.

In positions indicated by the dotted lines in FIG. 10A and the arrows inFIG. 10B, a portion from the first thin glass layer 101 to the firstplastic substrate 104 and a portion from the second thin glass layer 105to the second plastic substrate 107 are cut, thereby extracting aportion serving as a display device as shown in FIGS. 11A and 11B. Thesethin glass layers and plastic layers are simultaneously cut by using alaser. It is also possible to form a number of display devices at onceby using large non-alkaline glass substrates and plastic substrates andcutting these display devices in this step. When a CO₂ laser or a UV-YAGlaser of a secondary, tertiary, or quaternary harmonic component isused, the end faces are smoothly cut, and cracking of the thin glasslayers from these end faces can be prevented. If necessary, the endfaces can be further polished to form smoother surfaces. Furthermore,the plastic substrates and thin glass layers can be separately cut byselecting respective appropriate laser emission conditions and cuttingmethods, without being simultaneously cut.

As shown in FIGS. 12A and 12B, a liquid crystal is injected andencapsulated. A cell and liquid crystal reservoir are placed in a vacuumchamber, and the vacuum chamber is evacuated. After the chamber is wellevacuated, the injection hole 204 is brought into contact with theliquid crystal reservoir, and a liquid crystal 109 is injected bygradually restoring the atmospheric pressure. Instead of this vacuuminjection, suction injection may be performed by forming an injectionhole and suction hole. The liquid crystal can be a nematic liquidcrystal, cholesteric liquid crystal, ferroelectric liquid crystal, orpolymer dispersion liquid crystal. The injection hole 204 is sealed withan ultraviolet ray curable resin 203 or the like to complete the cell.

When a TN (Twisted Nematic) liquid crystal is used as the liquid crystal109 to obtain a transmitting type display device, as shown in FIGS. 13Aand 13B, polarizers 206 are formed on the outer surfaces of the firstand second plastic substrates 104 and 107. For example, when the secondplastic substrate 107 is used as a viewing side, the viewing angle canbe increased by adding a retardation film to the polarizer on this sideas in the conventional display devices. Also, when a reflecting plate isplaced in the liquid crystal cell to use this display device as areflecting type display device, the polarizer/retardation film 206 canbe formed only on the second plastic substrate 107. The polarizer canalso be omitted if the liquid crystal is in a scattering, interferencedisplay mode.

In this embodiment, the liquid crystal is injected after the cell isformed by bonding the plastic substrates to the thin glass layers.However, the following assembling method is also usable.

First, first and second non-alkaline glass substrates are thinned toform first and second thin glass layers, respectively. After first andsecond plastic substrates are bonded to these thin glass layers, asealing portion made of an ultraviolet ray curable adhesive is formed onone glass substrate. A liquid crystal is injected inside this sealingportion, and the sealing portion is covered with the other glasssubstrate and hardened to bond the two glass substrates. In this method,the injection hole 204 is not formed. FIG. 2A shows this arrangementhaving no injection hole. Otherwise, when two thick glass substrates arebonded as shown in FIG. 5, liquid crystal may be dropped onto thedisplay portion, and then the two glass substrates are sealed. After thesealing, the two glass substrates are polished to thin, followed byattaching the plastic substrates.

An example of the structure of an element usable in the active matrixtype display device of this embodiment will be described with referenceto FIGS. 14A and 14B. Although the display device has only two pixels inFIGS. 14A and 14B, a large number of pixels are actually formed in amatrix manner when viewed from the display surface.

Of the structure shown in FIGS. 14A and 14B, a portion different fromFIGS. 2A and 2B, i.e., a portion from the first thin glass layer 101 tothe second thin glass layer 105 will be explained.

On the first thin glass layer 101, first and second undercoat insulatingfilms 315 and 316 are stacked, and a polysilicon film including anactive layer 302 and source/drain regions 303 is formed in each pixel. Agate insulating film 304 is formed on the entire surface. On this gateinsulating film 304, gate electrodes 305 are formed in regionscorresponding to the active layers 302. On top of these gate electrodes305, an interlayer dielectric film 306 is formed on the entire surface.On this interlayer dielectric film 306, source electrodes 307 and drainelectrodes 308 connecting to the source/drain regions 303 via contactholes are formed.

Interconnections such as scanning/signal lines 320 are formed in thesame layer as the source electrodes 307 and drain electrodes 308.Covering these interconnections, a passivation film 321 is formed on theentire surface. On this passivation film 321, color filter layers 309are formed in regions corresponding to the individual pixels. On thesecolor filter layers 309, pixel electrodes 310 connecting to the drainelectrodes 308 via contact holes are formed. The pixel region in whichthese components are formed is surrounded by the seal 108, and thesecond thin glass layer 105 is placed on it. The common electrode 205 isformed on that surface of this second thin glass layer 105, whichopposes the pixel region. In the space surrounded by the pixel region,common electrode 205, and seal 108, a liquid crystal is injected to formthe liquid crystal layer 109.

In a region not participating in display, pillars 311 are formed everyfew pixels between the color filter layers 309 and common electrode 205.When external stress such as bending is applied, these pillars 311absorb the force. Although fiber-like pillars or pearl-like pillars canbe used, the pillars 311 are not limited to these forms.

In the peripheral region around the pixel region, electrodes 312 areformed in the same layer as the interconnections such as thescanning/signal lines 320, and connected to the common electrode 205 viatransfer conductors 313. These transfer conductors 313 are covered withresin protectors 314. Likewise, an anisotropic conductive sheet 319 isformed on the connecting pad electrode 110 which is formed in the samelayer as the interconnections such as the scanning/signal lines 320 inthe peripheral region. Interconnections 318 formed on the surface of aflexible substrate 317 are connected via this anisotropic conductivesheet 319.

A method of manufacturing the element having the structure as describedabove will be explained below. First, first and second undercoatinsulating films 315 and 316 are formed on a first non-alkaline glasssubstrate 201. The first undercoat insulating film 315 is formed to havea thickness of about 500 nm by using a silicon nitride film. The secondundercoat insulating film 316 is formed to have a thickness of about 100nm by using a silicon oxide film. These undercoat insulating films canbe a single layer, or other materials are also usable. The filmthickness is preferably about 100 to 500 nm.

On the second undercoat insulating film 316, an amorphous silicon filmwhich functions as active layers 302 and source/drain regions 303 isformed and patterned as a polysilicon layer after being crystallized byexcimer laser annealing. Instead of simple laser emission, it ispossible to use a technique by which an intensity profile is formed inlaser emission to cause lateral crystal growth and increase the grainsize, or a method which causes crystallization by heat without using anylaser. In this heat crystallization, crystallization may be performed byusing a metal such as Ni. The crystal grain size can be relativelysmall, e.g., about 0.1 μm to 10 μm, or as large as a single crystal. Thegrain boundary may be liked like a lattice. The source/drain regions 303are formed by introducing n- and p-type impurities by ion implantationor mass-separated ion injection. After gate electrodes (to be describedlater) are formed, it is possible to apply a self-aligned structureusing these gate electrodes as masks or apply an LDD (Lightly DopedDrain) structure in which a low-concentration doping region issandwiched between each of the source/drain region 303 containing ahigh-concentration impurity and active layer 302.

Subsequently, a silicon oxide film is formed as a gate insulating film304 on the entire surface by plasma CVD or the like. Furthermore, gateelectrodes 305 are formed in the regions corresponding to the activelayers 302 by using, e.g., a metal or alloy such as Mo, MoW, MoTa, Al,or Al—Cu, or highly doped silicon.

On these gate electrodes 305, an interlayer dielectric film 306 about300 nm to 1 μm thick is formed using a silicon oxide film or the like.As this interlayer dielectric film 306, an organic resin such aspolyimide can be used.

Source electrodes 307 and drain electrodes 308 connecting to thesource/drain regions 302 via through-holes formed in the gate insulatingfilm 304 and interlayer dielectric film 306 are formed on the interlayerdielectric film 306 by using, e.g., a metal or alloy such as Mo, MoW,MoTa, Al, or Al—Cu, or highly doped silicon.

In the same layer as the source electrodes 307 and drain electrodes 308,an electrode 312 which applies a potential to a connecting pad electrode110, inter-connections such as scanning/signal lines 320, and a commonelectrode 205 is formed using the same conductor material as describedabove.

On these electrodes and interconnections, a passivation film 321 isformed by plasma CVD or the like by using, e.g., a silicon nitride film.On this passivation film 321, a transparent organic insulating filmabout 1 μm to 4 μm thick may be formed by substantially the same patternas the passivation film 321, in order to improve the insulatingproperties and reduce the parasitic capacitance between theinterconnections.

On the passivation film 321, color filter layers 309 made of aphotosensitive organic resin are formed for individual pixels, therebyforming a color filter on array (COA) structure.

Pixel electrodes 310 are formed on the color filter layers 309. Thesepixel electrodes 310 are connected to the drain electrodes 308 viathrough-holes formed in the color filter layers 309 and passivation film321. When the COA structure is formed or the display device is atransmitting type display device, a transparent conductive film such asITO can be used as the pixel electrodes 310. When the display device isa reflecting type display device, a high-reflectivity metal such as Alor Ag can be used.

Since the surface on which the pixel electrodes 310 are formed isbrought into contact with a liquid crystal, an alignment film (notshown) is formed and subjected to rubbing. An alignment film (not shown)is also formed on the surface of the common electrode 205 made of atransparent conductive film such as ITO on a second non-alkaline glasssubstrate 202, and subjected to rubbing. Depending on the display mode,the common electrode 205 may be unnecessary, or the rubbing processusing an alignment film may be unnecessary. Also, the color filterstructure need not be the COA structure. For example, color filterlayers may be formed between the second non-alkaline glass substrate 202and common electrode 205, or overcoat layers may be formed on the colorfilter layers.

Not only the above-mentioned element structures are formed in theprospective pixel region but also transistors of control circuits suchas a signal line driver and scanning line driver can be integrated withthe pixel region. In this case, the control circuits are also bonded bythe pixel region adhesion layer 1002 having a low glass transitiontemperature.

On the connecting pad electrode 110 formed in the peripheral region, aflexible substrate 317 is placed via an anisotropic conductive film(ACF) and electrically connected by thermal compression bonding orthermal cure. This flexible substrate 317 is made of polyimide or PET,and an interconnection 318 made of a metal such as copper is formed. Inthis embodiment, a material having a high glass transition temperatureis used as the peripheral region adhesion layer 1001. Therefore,cracking does not easily occur even when thermal compression bonding isperformed. This connection can also be formed by a mechanical connectingmethod or wire bonding, instead of thermal compression bonding.

The electrode 312 which applies a potential to the common electrode 205is connected to the common electrode 205 via transfer conductors 313made of, e.g., conductive paste when the cell is formed. Resinprotectors 314 are formed around these transfer conductors 313 toreinforce the connection between the common electrode 305 and electrode312, thereby preventing poor connections if the display device is bentwhen in use. As this resin protector 314, an acryl-, epoxy-, orallyl-based ultraviolet ray curable resin is used. The first and secondnon-alkaline glass substrates may be thinned and bonded to the first andsecond plastic substrates after the cell is formed and a liquid crystalis injected. In this case, reinforcement of the connection by the resinprotectors 314 is more important. These resin protectors 314 can beformed not only around the transfer conductors 313 but also around theconnecting pad electrode 110.

In the active matrix type display device of this embodiment, after anelement circuit region is formed on a substrate such as a non-alkalineglass substrate which is highly resistant against heat, this substrateis thinned and bonded to a plastic substrate which is light in weight.The glass transition temperature of a pixel region adhesion layer is 30°C. (inclusive) to 80° C. (inclusive), and the glass transitiontemperature of a peripheral region adhesion layer is higher by 10° C. ormore than that of the pixel region adhesion layer, and is 80° C.(exclusive) to 200° C. (inclusive). The pixel region adhesion layer is asoft adhesive because its glass transition temperature is low.Therefore, when the plastic substrate contracts or expands because thedisplay device is bent, the force of this contraction or expansion canbe absorbed without being transmitted directly to the thin glass layer.

If the glass transition temperature of the pixel region adhesion layeris lower than 30° C., the temperature of the display device is alwaysequal to or higher than this glass transition temperature when thedevice is used at a room temperature, so no adhesion may be obtained. Onthe other hand, a glass transition temperature of higher than 80° C. istoo high, so the adhesion layer becomes hard.

Also, the peripheral region adhesion layer is a hard adhesive becauseits glass transition temperature is high. Therefore, the outermostregion of the thin glass layer which easily cracks can be stronglybonded. In addition, bonding to a flexible substrate for obtainingelectrical connection to the pixel region is performed in the peripheralregion by thermal compression bonding or the like. In this bonding, thehard peripheral region adhesion layer suppresses contraction andexpansion of the plastic substrate by heat, and also suppresses crackingof the thin glass layer by the pressure or the like during bonding.

If the glass transition temperature of this peripheral region adhesionlayer is about 80° C. or less, the adhesion layer may become a softadhesion layer depending on the use conditions. On the other hand, aglass transition temperature of higher than 200° C. is too high, so theplastic substrate may deform when it is bonded. By setting thedifference between the glass transition temperatures of the pixel regionadhesion layer and peripheral region adhesion layer to be 10° C. ormore, it is possible to maintain the hardness of the peripheral regionadhesion layer 1001 at higher temperatures, and protect the edges of thereadily breakable thin glass layer 105 against cracking.

Accordingly, as shown in FIG. 15, even when this display device is bentto form a curved surface having a radius R of curvature of about 50 mmto 150 mm, no cracks are formed in either the pixel region or peripheralregion. The weight can be reduced because the thickness of the plasticsubstrate and thin glass layer having the adhesion layer sandwichedbetween them is about 0.1 mm. Since the thin glass layer exists, theactive element circuit region is damaged little, and permeation of waterand gas such as oxygen can be prevented, so good element characteristicscan be obtained.

Also, when the display device is bent, tensile stress is produced on theconvex surface, and compression stress is produced on the concavesurface, so a plane having zero stress is formed between the twosurfaces. In this embodiment, the first and second thin glass layers areformed between the first and second plastic substrates. Therefore, thezero stress plane can be formed substantially between the first thinglass layer and second thin glass layer. This improves the bendingstrength of the display.

In the above embodiment, an active matrix in which one pixel is made upof one switching transistor, pixel electrode, and capacitive element isexplained. However, the present invention is also applicable to adisplay device which reduces the power consumption by using a memorycircuit (flip-flop; SRAM type, storage capacitor and driver transistor:DRAM type) for each pixel.

Furthermore, a control circuit, CPU, memory, and the like may beintegrated in addition to the scanning line and signal line drivers.These circuits, display electrodes, and the like can be collectivelyregarded as the components of the active element circuit region 102.Although these circuits inevitably require micropatterning, the use ofthe non-alkaline glass substrate which deforms little and has highprocessing accuracy allows formation of high-performance highlyintegrated circuits.

(Second Embodiment)

FIG. 16A is a plan view of an active matrix type display deviceaccording to the second embodiment. FIG. 16B is a sectional view takenalong a line 16B-16B in FIG. 16A. In this second embodiment, only adifference from the first embodiment will be explained, and adescription of similar parts will be omitted. This applies to eachembodiment to be described later.

In the active matrix type display device of this embodiment, an adhesionlayer is uniformly formed from one type of material. The difference fromthe first embodiment is that each of first and second plastic substrates104 and 107 is separated into a pixel region plastic substrate 1102 anda peripheral region plastic substrate 1101 formed around the pixelregion plastic substrate 1102. The linear expansion coefficient of thepixel region plastic substrate 1102 is 30 ppm/° C. (inclusive) to 300ppm/° C. (inclusive). The linear expansion coefficient of the peripheralregion plastic substrate 1101 is 1 ppm/° C. (inclusive) to 30 ppm/° C.(inclusive), which is about ⅔ or less that of the pixel region plasticsubstrate 1102.

Between the pixel region plastic substrate 1102 and the peripheralregion plastic substrate 1101 around the pixel region plastic substrate1102, a slight spacing is desirably formed as a margin againstextension.

The pixel region plastic substrate 1102 can be made of, e.g., PES,polycarbonate, polyolefin-based resin (e.g., Zeonor, cycloolefinpolymer, produced by Zeon Corporation), acrylic resin, polypropylene,polyester, or polyethylene, and can have a thickness of about 10 μm to200 μm. The peripheral region plastic substrate 1101 can be made of,e.g., PEN (PolyEthylene Naphthalate), polyethyleneterephthalate (PET),polyimide, filler-mixed epoxy resin, polyetheretherketone (PEEK),polysulfone (PSF), or polyetherimide (PEI), and can have a thickness ofabout 50 μm to 200 μm.

Even when a material having a large linear expansion coefficient isused, this linear expansion coefficient can be decreased by mixingfillers such as silica or alumina, so the material can be used as theperipheral region plastic substrate 1101. This peripheral region plasticsubstrate 1101 can be an opaque substrate because it does notparticipate in display.

The pixel region plastic substrate 1102 and peripheral region plasticsubstrate 1101 can have the same thickness, or the peripheral regionplastic substrate 1101 can be thicker. When the peripheral regionplastic substrate 1101 is made thicker, the peripheral region becomeshard to bend. This prevents stress concentration to a thin glass layer105 in this peripheral region and thus effectively makes this thin glasslayer 105 difficult to break.

In this embodiment, a PES film having a linear expansion coefficient ofabout 46 ppm/° C. is used as the pixel region plastic substrate 1102,and a PEN film having a linear expansion coefficient of about 11 ppm/°C. is used as the peripheral region plastic substrate 1101.

In this embodiment, after an element circuit region is formed onsubstrates such as non-alkaline glass substrates which are highlyresistant against heat, these substrates are thinned and bonded toplastic substrates which are light in weight. The linear expansioncoefficient of the pixel region plastic substrate is made as large asabout 30 ppm/° C. (inclusive) to 300 ppm/° C. (inclusive). The linearexpansion coefficient of the peripheral region plastic substrate is madeas small as 1 ppm/° C. (inclusive) to 30 ppm/° C. (exclusive), which is⅔ or less that of the pixel region plastic substrate.

If the linear expansion coefficient of the pixel region plasticsubstrate is less than 30 ppm/° C., this linear expansion coefficient istoo small, so the display device cannot be flexibly bent. If this linearexpansion coefficient is more than 300 ppm/° C., the difference from thelinear expansion coefficient of the thin glass layer becomes too large.This applies stress to the thin glass layer when the temperaturechanges.

If the linear expansion coefficient of the peripheral region plasticsubstrate is less than 1 ppm/° C., stress acting on the thin glass layercannot be reduced, so not only this thin glass layer but also theperipheral region plastic substrate may break. If this linear expansioncoefficient is more than 30 ppm/° C., the difference from the linearexpansion coefficient of the thin glass layer becomes too large. Thisallows easy cracking when heat is abruptly applied upon adhesion of aconnecting pad electrode and the like. Note that the above effects canbe obtained by setting the linear expansion coefficient of theperipheral region plastic substrate to be about ⅔ or less that of thepixel region plastic substrate.

Although the pixel region plastic substrate must be transparent, theproperties of organic resin make it difficult to obtain a plasticsubstrate having a small linear expansion coefficient such as that ofinorganic glass. Hence, a plastic substrate having a large linearexpansion coefficient as described above is used.

Since the linear expansion coefficient of the peripheral region plasticsubstrate is small, about ⅔ or less that of the pixel region plasticsubstrate, the linear expansion coefficients of the plastic substrateand thin glass layer are close in this peripheral region. Accordingly,the degree of expansion and contraction of this peripheral regionplastic substrate when the temperature changes while the display deviceis in use approaches that of the thin glass layer, so no stress isapplied to the thin glass layer. This raises the strength of the displaydevice. Also, the peripheral region does not easily expand or contracteven when temporarily heated and bonded by thermal compression bondingto a connecting pad electrode 110 formed in this peripheral region.

(Third Embodiment)

An active matrix type display device of the third embodiment has thecharacteristic features of both the first and second embodiments. Thatis, as shown in FIGS. 17A and 17B, an adhesion layer between a plasticsubstrate and thin glass layer is separated into a pixel region adhesionlayer 1002 and peripheral region adhesion layer 1001. In addition, theglass transition temperature of the pixel region adhesion layer 1002 is30° C. (inclusive) to 80° C. (inclusive), and the glass transitiontemperature of the peripheral region adhesion layer 1001 is higher by10° C. or more than that of the pixel region adhesion layer 1002, and is80° C. (exclusive) to 200° C. (inclusive).

Also, a plastic substrate is separated into a pixel region plasticsubstrate 1102 and a peripheral region plastic substrate 1101 formedaround the pixel region plastic substrate 1102. The linear expansioncoefficient of the pixel region plastic substrate 1102 is 30 ppm/° C.(inclusive) to 300 ppm/° C. (inclusive) The linear expansion coefficientof the peripheral region plastic substrate 1101 is about 1 ppm/° C.(inclusive) to 30 ppm/° C. (exclusive), which is about ⅔ or less that ofthe pixel region plastic substrate 1102. Furthermore, a slight spacingis formed between the pixel region plastic substrate 1102 and theperipheral region plastic substrate 1101.

With this construction, the effects of both the first and secondembodiments can be obtained. In addition, the materials andcharacteristics of both the adhesion layer and plastic substrate can beselected in the pixel region and peripheral region independently of eachother. This can maintain the element characteristics more preferably andmaintain the strength of the thin glass layer.

(Fourth Embodiment)

An active matrix type display device of the fourth embodiment is amodification of the second embodiment. As shown in FIG. 18, a portion ofa peripheral region plastic substrate 1103 covers a pixel region plasticsubstrate 1104 to form an overlapping portion.

More specifically, the linear expansion coefficient of the pixel regionplastic substrate is 30 ppm/° C. (inclusive) to 300 ppm/° C.(inclusive), and the linear expansion coefficient of the peripheralregion plastic substrate is about 1 ppm/° C. (inclusive) to 30 ppm/° C.(exclusive), which is about ⅔ or less that of the pixel region plasticsubstrate.

Even in this embodiment, the effects of the second embodiment can beobtained. Also, the whole of a thin glass layer can be reinforcedbecause there is no spacing between the pixel region plastic substrate1104 and peripheral region plastic substrate 1103.

(Fifth Embodiment)

An active matrix display device of the fifth embodiment shown in FIG. 19has the characteristic features of both the first and fourthembodiments. That is, an adhesion layer between a plastic substrate andthin glass layer is separated into a pixel region adhesion layer 1102having a glass transition temperature of 30° C. (inclusive) to 80° C.(inclusive), and a peripheral region adhesion layer 1101 having a glasstransition temperature which is higher by 10° C. or more than that ofthe pixel region adhesion layer and is 80° C. (exclusive) to 200° C.(inclusive) Also, the plastic substrate is separated into a pixel regionplastic substrate 1104 having a linear expansion coefficient of 30 ppm/°C. (inclusive) to 300 ppm/° C. (inclusive), and a peripheral regionplastic substrate 1103 formed around the pixel region plastic substrate1104 and having a linear expansion coefficient of 1 ppm/° C. (inclusive)to 30 ppm/° C. (exclusive) which is about ⅔ or less that of the pixelregion plastic substrate. A portion of the peripheral region plasticsubstrate 1103 covers the pixel region plastic substrate 1104 to form anoverlapping portion.

With this construction, the effects of both the first and fourthembodiments can be obtained. Furthermore, the materials andcharacteristics of both the adhesion layer and plastic substrate can beselected in the pixel region and peripheral region independently of eachother. This can maintain the element characteristics more preferably andmaintain the strength of the thin glass layer.

(Sixth Embodiment)

As shown in FIGS. 20A and 20B, an active matrix type display device ofthe sixth embodiment differs from the first embodiment in that asubstrate on which a common electrode 205 is formed comprises only aplastic substrate 501 with no thin glass layer. This configuration canreduce the number of manufacturing steps and can also reduce readilybreakable regions, in addition to the effects of the first embodiment.

A method of manufacturing the active matrix type display device of thisembodiment will be explained below with reference to FIGS. 21 to 29A and29B.

As in the first embodiment, an element circuit region 102 and connectingpad electrode 110 are formed on a first non-alkaline glass substrate201. After that, as shown in FIG. 21, this first non-alkaline glasssubstrate 201 having the element circuit region 102 and connecting padelectrode 110 formed on it is bonded to an intermediate substrate 602made of, e.g., glass or plastic, via a temporary adhesion layer 601. Asthis temporary adhesion layer 601, it is possible to use, e.g., awater-soluble photo-setting adhesive, or wax or a hot-melt adhesivewhich softens when heated or cooled. The temporary adhesion layer 601may be a pressure-sensitive adhesive or a film base having two surfacescoated with a pressure-sensitive adhesive. It is also possible to use aPET film or the like as the intermediate substrate 602, and aself-adhesive tape coated with a pressure-sensitive adhesive as thetemporary adhesion layer 601. As the intermediate substrate 602, thesame material and thickness as in the first embodiment can be used. Inthis embodiment, a glass substrate is used as the intermediate substrate602, and an ultraviolet ray curable, pressure-sensitive adhesive is usedas the temporary adhesion layer 601.

As shown in FIG. 22, the first non-alkaline glass substrate 201 ispolished by, e.g., mechanical polishing, chemical polishing, or chemicalmechanical polishing, thereby forming a first thin glass layer 101. Thefilm thickness of this first thin glass layer 101 is favorably about 5μm to 30 μm.

As shown in FIG. 23, the first thin glass layer 101 is bonded to a firstplastic substrate 104 via a first adhesion layer 103. In this firstadhesion layer 103, the characteristics of a peripheral region adhesionlayer 1001 outside a seal 108 are different from those of a pixel regionadhesion layer 1002. As in the first embodiment, the glass transitiontemperature of the pixel region adhesion layer 1002 is 30° C.(inclusive) to 80° C. (inclusive), and the glass transition temperatureof the peripheral region adhesion layer 1001 is higher by 10° C. oremore than that of the pixel region adhesion layer 1002, and is about 80°C. (exclusive) to 200° C. (inclusive).

As shown in FIGS. 24A and 24B, ultraviolet rays are radiated from theintermediate substrate side to lower the adhesion properties of thetemporary adhesion layer 601, thereby removing this temporary adhesionlayer 601. The result is a structure including the first plasticsubstrate 104, the first adhesion layer 103 (made up of the peripheralregion adhesion layer 1001 and pixel region adhesion layer 1002) on thefirst plastic substrate 104, the first thin glass layer 101 on the firstadhesion layer 103, the active element circuit region 102 on the firstthin glass layer 101, and the connecting pad electrode 110 on the firstthin glass layer 101.

Subsequently, in positions indicated by the dotted lines in FIG. 24A andthe arrows in FIG. 24B, a portion from the first thin glass layer 101 tothe first plastic substrate 104 is cut to extract a portion serving as adisplay device as shown in FIGS. 25A and 25B.

As shown in FIGS. 26A and 26B, a seal 502 is applied by a dispenser orthe like so as to surround a region in which pixels are present. At thesame time, a liquid crystal injection hole 204 is formed. The seal 502can be, e.g., an ultraviolet ray curable adhesive or thermosettingadhesive, and is preferably a material which hardens at lowtemperatures.

As shown in FIGS. 27A and 27B, a plastic substrate 501 on which a commonelectrode 205 is formed and the first non-alkaline glass substrate 201on which the active element circuit region 102 and connecting padelectrode 110 are formed are coupled and bonded by hardening the seal502, such that the common electrode 205 and active element circuitregion 102 oppose each other. Although the materials of the firstplastic substrate 104 and plastic substrate 501 are preferably the same,they may be different. The film thickness of the plastic substrate 501is favorably about 10 μm to 200 μm. This plastic substrate 501 can bemade of, e.g., an inorganic film such as a silicon oxide film or anorganic coating film such as an epoxy-based resin, and is preferablycoated. When coating the plastic substrate 501 effectively functions asa barrier against water and gas such as oxygen. Either one or both ofthe surfaces of this plastic substrate 501 can be coated. In thisembodiment, PES is used as the plastic substrate 501, and its surfaceopposing the common electrode 205 is coated with a silicon oxide filmabout 50 nm to 500 nm thick.

A liquid crystal layer 109 is formed by injecting the liquid crystalfrom the injection hole 204 shown in FIGS. 28A and 28B, and thisinjection hole 204 is sealed with a resin 203 as shown in FIGS. 29A and29B. In this structure shown in FIGS. 29A and 29B, polarizers 206 arebonded to the first plastic substrate 104 and plastic substrate 501.However, these polarizers need not be directly bonded to thesesubstrates.

The active matrix type display device of this embodiment can achieve thesame effects as in the first embodiment. Also, only the common electrode205 is formed, and the plastic substrate 501 is used as a substratewhich is not subjected to a high-temperature process. Since this furtherincreases the strength, the display device can be bent with a smallradius of curvature. Furthermore, the number of steps can be reducedbecause the plastic substrate 501 can be directly formed without anysteps of thinning and bonding a glass substrate.

(Seventh Embodiment)

As shown in FIGS. 30A and 30B, an active matrix type display device ofthe seventh embodiment differs from the first embodiment in that aplurality of adhesive resin members 701 are formed between an activeelement circuit region 102 and common electrode 205. These adhesiveresin members 701 are formed so that a first plastic substrate 104having the active element circuit region 102 formed on it and a secondplastic substrate 107 having the common electrode 205 formed on it arebonded not only on the perimeters of these substrates but also on theirinside surfaces. The adhesive resin members 701 are scattered atpredetermined intervals in the pixel region.

More specifically, before the first plastic substrate 104 on which theactive element circuit region 102 is formed and the second plasticsubstrate 107 on which the common electrode 205 is formed are coupled, aplurality of adhesive resin members are formed in appropriate positionson the active element circuit region 102. When these adhesive resinmembers 701 are formed on the active element circuit region 102 by usinga thermoplastic resin, the active element circuit region 102 and commonelectrode 205 are bonded by heat and pressure when the two substratesare coupled.

Pillars 311 formed in the first embodiment keep the distance between thetwo substrates, and these pillars 311 and the adhesive resin members 701can be independently formed. That is, both the pillars 311 and adhesiveresin members 701 may be formed. This construction is preferable sincethe height is held constant when the adhesive resin members 701 areprocessed with heat and pressure.

The adhesive resin members 701 need not be made of a single material.That is, it is possible to form adhesion layers on the upper and lowersurfaces of a resin spacer which hardly deforms, and attach these upperand lower adhesion layers to the active element circuit region 102 andcommon electrode 205.

The adhesive resin members 701 can be pillars having a diameter of about3 μm to 20 μm, ellipses, or a rib structure formed into stripes on thedisplay surface. Although the pitch (interval) of these adhesive resinmembers 701 can be one pixel, it can also be about 10 pixels. As thematerial of the adhesive resin members 701, it is possible to use, e.g.,an acrylic resin, polyethylene, polycarbonate, or so-called hot-melttype resin.

In this embodiment, the first and second plastic substrates are bondedand fixed not only on their perimeters but also on their insidesurfaces. Therefore, when the display device expands or contracts bybending, the stress can be effectively released to the opposingsubstrate via the adhesion resin members. This makes a thin glass layerdifficult to break.

(Eighth Embodiment)

As shown in FIGS. 31A and 31B, an active matrix type display device ofthe eighth embodiment differs from the first embodiment in that a firstplastic substrate 104 is larger than a first thin glass layer 101 whenviewed in a direction perpendicular to the substrate surface. This firstplastic substrate 104 is formed to the outside of the first thin glasslayer 101 on which an active element circuit region 102 is formed. Eachside of the first plastic substrate 104 is preferably larger by about 1mm to 10 mm than the corresponding side of the first thin glass layer101. This prevents impact to the first thin glass layer 101 in thedirections of the individual sides. A side (the left side in FIGS. 31Aand 31B) on which a connecting pad electrode 110 is formed has a regionwhere a second thin glass layer 105 is not present. This configurationis so effete as a local force is readily applied to the first thin glasslayer 101 in this region when the display device is bent. Therefore, thelarge first plastic substrate 104 is particularly effective in thisregion. Also, cracking of corners 802 can be prevented by cutting thefirst thin glass layer 101 in these corners 802 or rounding the corners802.

The active matrix type display device of this embodiment can bemanufactured by thinning a first non-alkaline glass substrate bymechanical polishing or the like to form a first thin glass layer 101,and bonding this first thin glass layer 101 to a plastic substrate 104having an area larger than the first thin glass layer 101 by using anadhesion layer 103 including a peripheral region adhesion layer 1001 andpixel region adhesion layer 1002. The display device can also be formedby first cutting a first thin glass layer 101 and first plasticsubstrate 104 to have relatively large areas, and then cutting only thefirst thin glass layer 101 with, e.g., a laser or diamond cutter fromthe side of this first thin glass layer 101.

A second plastic substrate 107 may be made larger than a second plasticsubstrate 105 when viewed in the direction perpendicular to thesubstrate surface. Alternatively, when viewed in the directionperpendicular to the substrate surface, the plastic layer need notlarger on every side but may be larger only on a side where theconnecting pad electrode 110 is formed.

(Ninth Embodiment)

As shown in FIGS. 32A and 32B, an active matrix type display device ofthe ninth embodiment differs from the first embodiment in that aprotective layer 901 protects not only the circumferences of transferconductors 313 but also at least a portion from a first plasticsubstrate 104, which includes a portion from a first adhesion layer 103to a second adhesion layer 106, to the circumference of a second plasticsubstrate 107 and the surface of a flexible substrate 317. In thisembodiment, after a liquid crystal is injected and a cell is sealed, anultraviolet ray curable resin such as an acryl-, allyl-, or epoxy-basedresin is applied as the protective layer 901 and hardened. As thisprotective layer 901, an elastic resin such as a rubber- orsilicone-based resin may be used. The regions covered with theprotective layer 901 need not be transparent because these regions arethe side surfaces of the display device and hence do not largelyparticipate in display. Referring to FIGS. 32A and 32B, the firstplastic substrate 104 is larger than a first thin glass layer 101 whenviewed in a direction perpendicular to the substrate surface. However,the first plastic substrate 104 and first thin glass layer 101 can havethe same size.

Those surfaces of the first thin glass layer 101 and a second thin glasslayer 105, which are bonded to the first and second plastic substrates104 and 107, respectively, are improved in strength because they arebonded. However, the strength of those surfaces of the first and secondthin glass layers 101 and 105, which oppose a liquid crystal layer 109,is slightly low. In this embodiment, in a region outside a seal 108 theprotective layer 901 protects and fixes the surfaces and side surfacesof the first and second thin glass layers 101 and 105, thereby improvingthe strength in the peripheral region. Even when the distance from theseal 108 to the edges of the first and second thin glass layers 101 and105 is about 1 mm to 10 mm, cracking is prevented and the strengthimproves. Also, the bending strength is twice or more that when noprotective layer 901 is formed. For example, when the film thickness ofthe first thin glass layer 101 was about 50 μm, the display device couldbe stably bent until the radius of curvature was about 100 mm with noprotective layer 901 formed. When the protective layer 901 was formedusing an acryl-based adhesive, the display device could be bent untilthe radius of curvature was about 50 mm.

(10th Embodiment)

As shown in FIG. 33, an active matrix type display device of the 10thembodiment differs from the ninth embodiment in that the peripheralregion is protected by using not only a protective layer 901 but also aplastic film 902. In particular, a plastic film 902 made of, e.g., PESor PEN is preferably bonded by using an adhesive on a first thin glasslayer 101 in a region in which a connecting pad electrode 110 andflexible substrate 317 are formed. As the material of this plastic film902, an acrylic resin, polyolefin resin, polyimide resin, or the likecan be used. Also, as the method of bonding the plastic film 902, meltadhesion of the material itself can also be used.

In this embodiment, the structure is thus further protected by theplastic film 902. Therefore, even if the strength is insufficient withthe protective layer 901 alone, the strength of the peripheral region onthe first thin glass layer can be increased.

(11th Embodiment)

In the 11th embodiment, as shown in FIG. 34, a structure in which apartial reinforcing substrate is formed on the rear surface of a firstplastic substrate will be explained as a modification of the secondembodiment.

A first thin glass layer 101 having an active element circuit region 102formed on it is formed in the same manner as in the second embodiment.On the entire rear surface of this first thin glass layer 101, a firstplastic substrate 1201 is bonded via an adhesion layer 103. Thisadhesion layer 103 can be a photo-setting adhesive such as anultraviolet ray curable resin, a two-part adhesive, a thermosettingadhesive, or the like. The method of adhesion can be any known methodand is not particularly limited.

A third plastic substrate 1202 for reinforcement is bonded to a regionof the first plastic substrate 1201 in which a connecting pad 110 is tobe formed. The linear expansion coefficient of this third plasticsubstrate is smaller than that of the first plastic substrate. In thisembodiment, a plastic substrate made of, e.g., PEN whose linearexpansion coefficient is as small as 2 ppm/° C. to 40 ppm/° C. is usedas the third plastic substrate 1202.

As the first plastic substrate, a transparent substrate having a linearexpansion coefficient of 30 ppm/° C. (inclusive) to 60 ppm/° C.(inclusive), which is larger than that of the third plastic substrate,is used. The first and third plastic substrates may be bonded by amethod which melts the substrates by heat fusing or a solvent, insteadof the method using an adhesive. The thickness of the first plasticsubstrate is 10 μm to 100 μm. Although the third plastic substrate ispreferably thicker than the first plastic substrate, it may be thin, sothat the thickness of this third plastic substrate is desirably as largeas 50 μm to 200 μm.

In this embodiment, the third plastic substrate reduces stressapplication with respect to heat in the peripheral portion and makesthermal deformation hard to occur. The reliability of connection alsoimproves. In particular, the strength of a portion where opposingsubstrates 107 and 105 do not exist improves. Additionally, the firstplastic substrate can be bonded to the entire surface of the first thinglass layer 101. So, the strength rises when the first plastic substrateis bonded, and this improves the manufacturing yield. This alsofacilitates bonding the first plastic substrate on a large substrate.The third plastic substrate may be bonded after a cell is cut out.

FIG. 35 is a modification of the 11th embodiment. This modification isthe same as FIG. 34 except that a fourth plastic substrate 1203 forreinforcement is formed in a peripheral portion, in addition to a padportion. This reduces deformation of the peripheral portion.

FIG. 36 shows another modification. An adhesion layer istwo-dimensionally split into two parts. As in the first embodiment, afirst adhesion layer 1301 has a high glass transition temperature, and asecond adhesion layer 1302 has a low glass transition temperature. Afirst plastic substrate 1201 is bonded to the entire surface of a firstthin glass plate 101, and third and fourth plastic substrates 1202 and1203 are bonded to a pad portion and peripheral portion, respectively.The third and fourth plastic substrates desirably have a small linearexpansion coefficient and can effectively suppress deformation of thefirst plastic substrate together with the adhesion layer 1301.

The adhesion layer 1301 has a glass transition temperature of 90° C. to110° C., a linear expansion coefficient of 10 ppm/° C. to 70 ppm/° C.,and a Young's modulus of 0.8 GPa to 2 GPa. The adhesion layer 1302 has aglass transition temperature of 45° C. to 60° C., a linear expansioncoefficient of 100 ppm/° C. to 300 ppm/° C., and a Young's modulus of0.4 GPa to 0.8 GPa. The film thickness is 5 μm to 50 μm. These adhesionlayers can be selected in the same manner as in the previousembodiments.

On the first thin glass layer 101, a second thin glass layer 105 andsecond plastic substrate 107 are formed via a seal 108, and a liquidcrystal layer 109 is placed. This is the same as in the firstembodiment.

(12th Embodiment)

In the first to 11th embodiments described above, a liquid crystal isused as a display part. However, the display part is not restricted to aliquid crystal. As shown in FIGS. 37A and 37B, the 12th embodiment usesan organic EL as the display part. When an organic EL is used, it ispreferable to use a current-driven type peripheral driver and, in eachpixel, a 2- to 6-transistor selecting switch, current supply drivingtransistor, and transistor characteristic variation correction circuit.These circuit configurations can be any conventionally used circuits, sodetails of these circuits will be omitted. Electrophoretic elements maybe used in the display part. Even when a liquid crystal is used as thedisplay part, it is also possible to use a method in which a pair ofcomb-like pixel electrodes are formed on the side of an element circuitregion without forming any counter common electrode, and electric chargeis applied in the direction of the display surface to drive the liquidcrystal.

Of the arrangement shown in FIG. 37B, only that structure above apassivation film 321, which is different from FIG. 14B will beexplained.

As shown in FIG. 37B, pixel electrodes 310 connecting to drainelectrodes 308 via through holes formed in the passivation film 321 areformed on the passivation film 321, and an insulating layer 1202 isformed on an entire prospective pixel region. In holes formed in thoseregions of the insulating layer 1202, which correspond to the pixelelectrodes 310, a hole transporting layer 1203, light emitting layer1204, and electron injecting layer 1205 are stacked in this order. Acommon electrode 1206 is then formed on the entire surface. This commonelectrode 1206 electrically connects to the electron injecting layer1205 of each pixel and also electrically connects to an electrode 312. Asecond thin glass layer 105 is formed on a gap 1201 above the commonelectrode 1206. A spacer 1207 is formed between the insulating layer1202 and second thin glass layer 105 to hold the distance between thesubstrates.

In a method of manufacturing the active matrix type display device ofthis embodiment, the arrangement above the passivation film will beexplained.

Through holes are formed in the passivation film 321, and pixelelectrodes which connect to the drain electrodes 308 through thesethrough holes are formed by a transparent conductive film made of, e.g.,ITO. An acryl-based photosensitive resin is formed on the entire surfaceto have a film thickness of about 2 μm to 8 μm, thereby forming aninsulating layer 1202. This insulating layer 1202 is irradiated withlight to form holes in regions corresponding to the pixel electrodes310. Into each hole, droplets of a hole transporting layer 1203, lightemitting layer 1204, and electron injecting layer 1205 are sequentiallydropped by an inkjet method or the like. The thickness of the insulatinglayer 1202 is preferably large because the hole transporting layer 1203,light emitting layer 1204, and electron injecting layer 1205 are stackedin the holes described above. As the light emitting layer 1204, apolyparaphenylenevinylene-, polyallylene-, or polyfluorene-based lightemitting material can be used. As the hole transporting layer 1203,polyethylene-dioxythiophene-polystyrene-sulfonic acid salt (PEDT/PSS) orthe like can be used. As the electron injecting layer 1205, it ispossible to use, e.g., an oxadiazole derivative (OXD), PBD, triazoles(TAZ), phenyl-quinoxaline, or Alq. However, the materials are notlimited to those enumerated above.

Subsequently, a common electrode 1206 electrically connecting to theelectron injecting layer 1205 of each pixel is formed on the entiresurface. This common electrode electrically connects to the electrode312 to apply the voltage of this electrode 312 to the electron injectinglayer 1205. As the common electrode 1206, it is possible to use, e.g., ametal or alloy having a low work function and covered with a metal oralloy for a line, Al—Ca, Al—Li, or ITO. It is also possible to switchthe electron injecting layer and hole transporting layer, i.e., to stackthe electron injecting layer, light emitting layer, and holetransporting layer in this order from below. Furthermore, a transparentcommon electrode may be used to emit light from the upper surface.

A seal 108 is formed around the pixel region. An array substrate (formedby bonding a first plastic substrate 104 to a first thin glass layer101) on which parts up to the common electrode 1206 are formed is bondedto an opposing substrate (formed by bonding a second plastic substrate107 to a second thin glass layer 105). As the seal 108, it is possibleto use, e.g., an ultraviolet ray curable resin mixed with inorganicfillers having a reduced gas permeability can be used. After the twosubstrates are coupled, this seal 108 is hardened and bonded byirradiation with ultraviolet rays. A gas such as dried nitrogen can besealed in a gap 1201 between the two substrates. Furthermore, a getteragent for water or oxygen, e.g., a desiccant or oxygen absorbent may beformed on the surface or on a portion of the second thin glass layer105, and high-purity grease or organic liquid may be sealed.

A display device using an organic EL must be entirely sealed to preventdeterioration of the electrodes, light emitting layers 1204, and thelike under the influence of the atmosphere such as water and oxygen. Inthis embodiment, the first and second thin glass layers 101 and 105 canprevent permeation of, e.g., water and oxygen from the substratesurfaces. These thin glass layers are preferably made of non-alkalineglass. A thin glass layer about 1 μm to 150 μm thick can preventpermeation of gases. When the spacer 1207 is formed on the insulatinglayer 1202 by using a photosensitive organic resin or the like, thedistance between the two layers can be held constant. As in the firstembodiment, the characteristics of the adhesion layer in the pixelregion are different from those of the adhesion layer in the peripheralregion. Accordingly, the same effects as in the first embodiment canalso be obtained.

The sixth to 12th embodiments described above are explained asmodifications of the first embodiment, but these embodiments are notlimited to modifications of the first embodiment. That is, the sixth to12th embodiments may be modifications of the second embodiment in whichthe properties of the plastic substrate in the pixel region aredifferent from those of the plastic substrate in the peripheral region,modifications of the third embodiment in which the properties of boththe adhesion layer and plastic substrate in the pixel region aredifferent from those of the adhesion layer and plastic substrate in theperipheral region, modifications of the fourth embodiment in which theproperties of the plastic substrate in the pixel region are differentfrom those of the plastic substrate in the peripheral region and theplastic substrates in these two regions overlap each other, ormodifications of the fifth embodiment in which the properties of boththe adhesion layer and plastic substrate in the pixel region aredifferent from those of the adhesion layer and plastic substrate in theperipheral region and the plastic substrates in these two regionsoverlap each other.

Furthermore, the display device manufacturing method of each embodimentmay be the method of the first embodiment by which first and secondnon-alkaline glass substrates are first coupled and then thinned to formthin glass layers, or may be a method by which a first non-alkalineglass substrate having an element circuit region and the like formed onit is first bonded to an intermediate substrate via a temporary adhesionlayer and then thinned to form a first thin glass layer, this first thinglass layer is bonded to a first plastic substrate, and then thetemporary adhesion layer is removed. In this case, the manufacturingsteps as shown in FIGS. 3A and 3B through 6A and 6B is firstly performedto thin the element formation substrate 201, thereby obtaining the thinglass substrate 101. Then, as shown in FIGS. 27A and 27B, the opposingsubstrate 501, for example, is opposed to the thin glass substrate 101to form a display cell. Thereafter, the plastic substrate 104 is bondedto the thin glass substrate 101 to complete a display device.

As has been described in detail above, the present invention can providean active matrix type display device by which active elements can beformed with high yield by using a plastic substrate which is light inweight, and a method of manufacturing the same.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1-19. (canceled)
 20. A display device manufacturing method comprising:forming active elements in one-to-one relation with pixels on an elementformation substrate made of glass; thinning the element formationsubstrate by polishing after said forming the active elements; bondingthe element formation substrate to a plastic substrate via a firstadhesion layer in a pixel region and via a second adhesion layer in aperipheral region outside of the pixel region; and opposing the elementformation substrate with an opposing substrate to form a display partdriven by the active elements and displaying an image in units ofpixels.
 21. The method according to claim 20, wherein a glass transitiontemperature of the first adhesion layer is 30° C. (inclusive) to 80° C.(inclusive), and a glass transition temperature of the second adhesionlayer is higher by not less than 10° C. than that of the first adhesionlayer, and is 80° C. (exclusive) to 200° C. (inclusive).
 22. The methodaccording to claim 20, wherein said thinning the element formationsubstrate is performed after said opposing the element formationsubstrate with the opposing substrate, and said bonding the plasticsubstrate to the element formation substrate is performed after saidthinning the element formation substrate.
 23. The method according toclaim 20, further comprising thinning the opposing substrate made ofglass after said opposing the element formation substrate with theopposing substrate.
 24. A display device manufacturing methodcomprising: forming active elements in one-to-one relation with pixelson an element formation substrate made of glass; thinning the elementformation substrate by polishing after said forming the active elements;bonding a first plastic substrate to the element formation substrate atleast in a pixel region via an adhesion layer, and bonding a thirdplastic substrate to the element formation substrate or the firstplastic substrate in a peripheral region outside of the pixel region viathe adhesion layer; and opposing the element formation substrate with anopposing substrate to form a display part driven by the active elementsand displaying an image in units of pixels.
 25. The method according toclaim 24, wherein a linear expansion coefficient of the first plasticsubstrate is 30 ppm/° C. (inclusive) to 300 ppm/° C. (inclusive), and alinear expansion coefficient of the third plastic substrate is not morethan ⅔ that of the first plastic layer, and is 1 ppm/° C. (inclusive) to30 ppm/° C. (exclusive).
 26. The method according to claim 24, whereinsaid thinning the element formation substrate is performed after saidopposing the element formation substrate with the opposing substrate,and said bonding the first and the third plastic substrate to theelement formation substrate is performed after said thinning the elementformation substrate.
 27. The method according to claim 24, furthercomprising thinning the opposing substrate made of glass after saidopposing the element formation substrate with the opposing substrate.